1. Field of the Invention
This invention generally relates to an MEMS probe card, and more particularly to an MEMS probe card with multi-layer structure.
2. Description of the Related Art
Semiconductor devices have to be tested before packaging. A wafer is put in a testing machine with vertical probe tips, then utilizing the probe tips of a probe card to probe a plurality of bumps of input and output signal pads of the wafer. However, because the bumps disposed on the wafer have manufacturing variations, the heights of the bumps are different with each other, especially those bumps need to be reflowed to ball bumps will have larger variations in height. To ensure the probe tips to electrically contact the bumps effectively, the probe tips may be designed to have elasticity so as to improve the electrical coupling between the probe tips and the bumps.
FIG. 1 shows a conventional micro-electro-mechanical system (MEMS) probe card which is disclosed in U.S. Pat. No. 6,084,420. An MEMS probe assembly 120 is disposed on a testing pad 110, and the MEMS probe assembly 120 has a plurality of bridge elements 121, a plurality of supporting members 122 and a probe tip 123. The bridge elements 121 are laterally T-shaped and arranged in a single layer outward radiated structure, two sides of a head 121a of each bridge element 121 are respectively connected to the supporting members 122, tails 121b of the bridge elements 121 are connected together, and the probe tip 123 is disposed on the conjunction of the tails 121b of the bridge elements 121. According to the support to the probe tip 123 with the bridge elements 121 and the supporting members 122, the MEMS probe assembly 120 may have longitudinal elasticity. However, because the bridge elements 121 are arranged in single layer, they may have a limited elastic buffer. Moreover, the arrangement of the probe assembly with outward radiated structure may cause wasting of room and relatively decrease the counts of the MEMS probes assembly 120 on the probe card.